The present invention relates generally to a telephone terminal device, and more specifically to an improvement in a power supply method therefor.
Certain telephone terminal devices such as an automatic telephone terminal answering device (referred to as terminal answering device, hereinafter) are provided with an automatic answering circuit and a message recording/playing back circuit, with which a telephone line (office line) can be acquired automatically in response to a call signal; an outgoing message (referred to as OGM) is played back; an incoming message from a caller (referred to as ICM) is recorded as a service to the telephone caller; and further an OGM is recorded or an ICM is played back in call waiting mode as a service to the telephone subscriber. In the telephone terminal device such as a terminal answering device provided with the automatic answering circuit and the message recording/playing back circuit, it has been conventional to supply power to these circuits from a commercial power source through an AC adapter.
In the conventional telephone terminal device so constructed as to receive power from a commercial power source, however, there exists a problem in that the device will not be operative during power failure or is unusable at a place where the commercial power source is not available. To overcome the above-mentioned problem, it may be possible to activate the automatic answering circuit and the message recording/playing back circuit by a built-in battery. In this case, however, there exists another problem in that the terminal device will not be operative after many hours of battery consumption.